Recently, there is extensively used an endoscope whereby organs within a body cavity can be observed by inserting an elongate insertable part into the body cavity or, as required, various curing treatments can be made by using a treating tool inserted through a treating tool channel.
There are also suggested various electronic endoscopes wherein such solid state imaging device as a charge coupled device (CCD) is used for the imaging means. There are advantages that, as compared with a fiberscope, such electronic endoscope is higher in the resolution, is easier to record and reproduce picture images and is easier in such picture image processes as the magnification of picture images and the comparison of two picture surfaces.
The conventional electronic endoscope is formed as shown, for example, in FIG. 1.
That is to say, an image forming optical system 2 consisting of an objective lens or the like is provided in the tip part 1 of an endoscope insertable part and a solid state imaging device 3 is arranged in the image forming position of this image forming optical system. This solid state imaging device 3 is driven by a driving signal from a driving pulse generating circuit within a video processor 4 connected to the endoscope. The signal read out is processed to be a video signal by a video signal processing circuit within the above mentioned video processor 4. The video signal output from this video signal processing circuit is input into such displaying apparatus 5 as a color CRT monitor in which the observed image of an object 6 is displayed. The picture image displayed in the above mentioned displaying apparatus 5 is such right image as is shown in FIG. 2.
Now, shown in FIG. 1 is a straight viewing type endoscope. As shown in FIG. 3, there is already a side viewing adapter 7 enabling straight viewing by being fitted to the tip part 1 of the above mentioned straight viewing type endoscope. This side viewing adapter 7 contains such reflecting member 8 as a mirror or prism. The image of a side visual fields is reflected by this reflecting member 8 and can be formed in a solid state imaging device through the image forming optical system 2.
Now, when the object is imaged by fitting the above mentioned side viewing adapter 7, the object image will be reflected by the above mentioned reflecting member 8 and therefore, as shown in FIG. 2 (b), an image (back image) inverted only vertically (or only horizontally) will be displayed. It is hard to see as it is. Therefore, conventionally, as shown, for example, in the gazette of a Japanese patent laid open No. 50546/1986, by using a plurality of memories memorizing the video signals in one horizontal scanning period, the signals in each horizontal scanning period are read out from the direction reverse to that at the time of writing in to invert the image horizontally.
An example of the electronic endoscope apparatus provided with such means of inverting the image is shown in FIG. 4.
As shown in FIG. 4, the signal read out of the solid state imaging device 3 driven by the driving signal from a driving pulse generating circuit 11 within a video processor 10 is processed to be .gamma.-corrected or the like in a video signal processing circuit 12 within the above mentioned video processor 10 and is converted to digital data by an A/D converter 13. The digital data are switched to a 1H memory 15A and 1H memory 15B every horizontal scanning period by a switching circuit 14 and are delivered. These 1H memory 15A and 1H memory 15B memorize respectively time series data in one horizontal scanning period on the basis of address signals output respectively from address controllers 16A and 16B. In this horizontal scanning period in which the data are being written into the 1H memory 15A by a switching circuit 17, the data within the 1H memory 15B are read out and are delivered to the D/A converter 18. On the other hand, in the horizontal scanning period in which the data are being written into the 1H memory 15B, the data within the 1H memory 15A are read out, are delivered to the D/A converter 18, are converted to an analogue video signal by this D/A converter 18 and are delivered to a displaying apparatus. This operation is repeated every horizontal scanning period. The above mentioned address controllers 16A and 16B are formed respectively of counters or the like and sequentially vary the 1H memories 15A and 15B in time series. Also, in these address controllers 16A and 16B, the address variation is switched and controlled to be in the increasing direction or decreasing direction by an inversion and non-inversion control circuit 19.
In such electronic endoscope apparatus, as shown in FIG. 4, in the case of a straight viewing observation, the address controllers 16A and 16B will sequentially vary the memory addresses exactly the same at the time of respectively writing in and reading out the data. That is to say, the time series data in each respective horizontal scanning period are read out in exactly the same order as the order of writing in. As a result, in the displaying apparatus 5, as shown in FIG. 5 (a), a right image will be displayed. On the other hand, as shown in FIG. 3, in the case of a side viewing observation by using the side viewing adapter 7, by the control of the inversion and non-inversion control circuit, the above mentioned address controllers 16A and 16B both vary the addresses in the direction reverse to that of writing in or reading out the data. That is to say, for example, if in response to the time series data in one horizontal scanning period, the addresses are varied from 0 to N in the order of 1, 2, . . . and are written into the memories 15A and 15B, at the time of reading out the memories 15A and 15B, the addresses will be varied reversely from N to N-1, N-2, . . . 0. As a result, the picture image displayed in the displaying apparatus 5 will be inverted horizontally in the right and left with respect to the imaged image. That is to say, the displayed picture image in the case that exactly the same signal process as in the case of straight viewing is made white using the side viewing adapter 7 is such vertically inverted image as is shown in FIG. 2 (b). Therefore, the displayed picture image in case the above described signal process is made by using the above mentioned video processor 10 will be an image inverted both vertically and horizontally as shown in FIG. 5 (b). That image is the same right image as is shown in FIG. 2 (a) or 5 (a) and is a practically satisfactory image.
However, in the prior art example shown in FIG. 4, the address controllers 16A and 16B are required. Each of these address controllers 16A and 16B must be formed of a synchronous reversible counter of about 10 fits and must be operated at a speed high enough to cover the band of the video signal. Such circuit is complicated and large. If such large counter operates during the horizontal scanning period, digital signals of various frequencies generated there will be likely to mix as noises into the video signal, various vertical stripes will appear on the displayed picture image and the picture quality will remarkably deteriorate.
Thus, in the conventional means of obtaining right images, there are problems that the circuits are so complicated that, only for the function of converting a back image to a right image, the video processor becomes large in the size and high in the cost and the picture quality deteriorates.
In the gazette of a Japanese patent laid open No. 46922/1983, a solid state imaging device is provided with a series line reading out driving circuit in which the direction of horizontally scanning the imaging surface is made reverse to the conventional scanning direction and, in case the image imaged on the imaging surface of the solid state imaging device is a back image, the imaging surface should be scanned reversely to the conventional scanning direction to read out the picture image signal.
Further, in U.S. Pat. No. 4,677,470, there are two 1-line memory groups A and B and, in case A is reading out the address moving up and down for each horizontal line, B will write in the address and, in case A is writing in the address, B will read out the address. As a result, the outputs are alternately inverted horizontally on the right and left for each horizontal line and therefore the technique of continuously outputting output signals of right images is disclosed.